Phase seems to me to be the most immediate potential problem. If the two locations create phase cancellation, calibrating them separately and combining them would not reveal that cancellation. Beyond that, I get into a level of detail that I don't trust myself to be sufficiently informed on, but I could see EQ adjustments being made to help one sub overcome a dip or reduce a peak that could be naturally smoothed out by interaction with the other sub (which, due to a different location within the room, might be cancelling out or lessening the magnitude of the problem spots for that first sub). In both scenarios, adjusting the two subs as a unified pair would be quicker, easier, and better sounding.

It reminds me of one SMS-1 owner who had multiple subwoofers and found that his placement of those subs had already achieved enough "flattening" that using a separate sub EQ gained him nothing. Looking at each sub individually would have led him to do a lot of EQ work, whereas looking at the whole revealed that he needed very little actual adjustment.


The pessimistic answer to that would be "because they sound cool and can be sold more easily as a result." There are other less-than-optimal product ideas that are very popular for marketing reasons, or sound popular at first but eventually fade away. (Case in point: TV manufacturers are starting to re-consider "smart TV's" with all sorts of network functions built in - leaving such functions for a Blu-ray player or standalone device or receiver, all of which are duplicating those functions these days, apparently made more sense to consumers.)


Since Audyssey already had the ability in the firmware, it sounds like they just left it there for greater flexibility. And technically it can work - it just may take more effort and may yield a result that is no better than the alternative.


Do the DD subs have the ability to slave one sub to the other, or do you have to set up each individually? Since they built the EQ hardware into the sub, you kind of have to EQ each separately unless there's a master/slave option.